The use of skin lightening cosmetics varies significantly among cultures. In Western countries, for example, skin lighteners are applied for the prevention or treatment of melasma, freckles (lentigo aesticva), age spots (lentigo senilis), or to “even out” skin tone in general. In Asian and African nations, the primary use of skin lighteners is to make the skin whiter, lighter and/or brighter.
The pigments contributing to the color of the skin are carotenoids, hemoglobin and melanin. Melanin, however, is produced in melanocytes which are the pigment-forming cells in the basal layers of the epidermis and, as such, will largely determine the color of the skin. Numerous cosmetic compositions have recently been developed to reduce the amount of melanin in the skin. The majority of these products achieve reduction in melanin by inhibiting tyrosinase, which is apparently the only essential enzyme in the biosynthesis of melanin.
There are a number available tyrosinase inhibitors used in cosmetic compositions. One of the first tyrosinase inhibitors used in skin lightening was hydroquinone, used either alone or in combination with other functional materials such as kojic acid, as described in U.S. Pat. No. 5,279,834 (Meybek). These materials apparently give only temporary effect, and hyperpigmentation returns if use of the described composition is discontinued.
More recently, bearberry, arbutin and rutin (usually derived from botanical sources) have been found to be effective tyrosinase inhibitors, as disclosed in U.S. Pat. Nos. 5,980,904 (Leverett), 6,123,959 (Jones), and 5,882,658 (Simon), respectively. These preparations seem to have a cumulative effect and, with continued use, hyperpigmentation may be controlled with less frequent application of the compositions.
Functional tyrosinase inhibitors such as those mentioned above have also been used in combination with other agents. U.S. Pat. No. 5,747,006 (Dornoff) discusses a combination of acerola cherry fermentate with bearberry extract, arbutin, kojic acid and various free radical scavergers and/or botanical extracts. Similarly, U.S. Pat. Nos. 6,077,503 (Dornoff) and 4,818,768 (Nazzaro-Porro) disclose the use of mercaptodexran and mercapto-derivatives of dicarboxylic acid, respectively, in combination with free radical scavergers, arbutin, kojic acid and/or various botanical extracts.
Compositions such as the above seem to be effective, to varying degrees, in whitening or lightening the skin, but room for improvement still exists.